SiC-Based Resonant Converters With ZVS Operated in MHz Range Driving Rapidly Variable Loads: Inductively Coupled Plasmas as a Case of Study

Wide band-gap resonant converters operating with zero voltage switching (ZVS) recently proved the conversion of up to 25 \,\mathrm{k}\mathrm{W} at 3 \,\mathrm{M}\mathrm{Hz} with an efficiency of \approx94 \%. This is of special interest for any application where power in middle frequency range is required since typically achieved efficiencies for those frequencies are in the range of 60\% \hbox{--}70\%. Inductively coupled plasma (ICP) based applications would significantly benefit from this fact, but they entail special driving challenges. ICP loads exhibit strong impedance variations during ignition and operation, which means a high limitation factor when driving them with resonant converters. This article offers a deeper look into this topic through the example of a 10 \,\mathrm{Pa} Xenon lamp. The ignition transient is measured and analyzed while driving the system with a Silicon Carbide (SiC)-based resonant converter. An FEM simulation modeling the electromagnetic, thermal, mechanical, and plasma properties is also performed. The results are contrasted with the corresponding measurements showing as well the simulation usefulness as a design tool. Theoretical calculations of the intrinsic limits for ZVS resonant power conversion are also offered. This provides an insight into which analysis and control methods would make ICP loads compatible with these converters and, therefore, able to benefit completely from their efficiency and power density benefits.